I HAVE DV2150, LOVE IT BUT AS OF LAST WEEK THE TIME IS 1 HOUR AHEAD. IHAVE SET IT UP LOTS OF TIMES. THE HOUR WILL BE SET UP AND AFTER IT IS SET IT WILL GO BACK TO THE 1 HOUR AHEAD. HOPE YOU CAN HELP WITH THIS. I ORIGINALLY HAD YOUR DOUBLE SET UP SO YOU SEE I LIKE YOUR PRODUCT.

In the UK the clocks go forward 1 hour at 1am on the last Sunday in March, and back 1 hour at 2am on the last Sunday in October. The period when the clocks are 1 hour ahead is called British Summer Time (BST). There's more daylight in the evenings and less in the mornings (sometimes called Daylight Saving Time).

did you get the update for the new DST shift that happened a week early this year?

First start with the reset button, clears out all past commands.
First the clock has to be set to the proper day and time, It might be in the 24 system versus AM and PM you can find this out by stepping through all the hours when the time comes on. To set clock press Set and see what is flashing, if it is the day, scroll to the right day and hit set, now time should flash scroll to right hour, press set, right minutes, press set, right seconds, press set; Now the clock should be set.
Next you do the programs you want again go through same process, hit program 1 should flash press set, now the days should flash, scroll through till you have the right combo of days, one day, all days of week, Sat, Sun, then last the whole week will flash, if that is the one you want then press set, now press set and the times should flash for hour.
pick the time you want to come on, hit set for hour, minute, second, then hit set again now hit the program button again and it should say off, go through the same steps and set hour, minute second then hit set for last time. In a few minutes it should change to reading the time on the screen. Then you have to wait and see if it works. To do a mini version, see if it will work get a lamp plug in set all the above but use a very short on off time like 4 or 5 mins, then you will know if it is going to work right. then set for the correct time. good luck hope it helps. If it all messes up just hit reset and start all over, REMEMBER it can't so anything until the time of day is set right that's the starting point.

Do you have a setting for the power line frequency? Some devices get their timebase from the power line frequency and if your powerline is 60 Hz, but you have it set on 50 Hz, then it will speed it up because of the 10 extra cycles per second.

Thank you for very clear question, and timer identification.
1) I don't have repair for defective timer.
http://waterheatertimer.org/Intermatic-timers-and-manuals.html#DT300
http://waterheatertimer.org/pdf/DT300-series-manual.pdf

2) Choose DT300 format
#3 says to press-and-hold CLOCK button until display shows 24H or 12H
Then release CLOCK button.
Next press HOUR button to select either 12H or 24H
This lets you choose am-pm format -or- choose military-time format where 11pm is 23

3) Set current time
Press-and-hold CLOCK button throughout whole current time setting.
Do not release CLOCK button until current time settings are finished.
Next, press HOUR button, and then MINUTE button, and then DAYS button until current hour, minute and day display.
Then release CLOCK button.
If this step does not work, then timer has gone bad.
Replace with locally available Utilitec 155671 from Lowes or Westek TE06WHB from Target
http://waterheatertimer.org/Woods-timers-and-manuals.html#59377

4) How to set DT300 timer program for full week of operation.
Each program requires you to set program 1 ON time and program 1 OFF time
Be careful to avoid program conflicts and overlaps so timer works as expected.

For program 1 ON time, you press PROGRAM button until 1 and ON display.
Release Program button.
Then select hour, minute and days. In this case you want all days of week, so you keep pressing DAYs button until whole week displays: Mo Tu We Th Fr Sa Su

Then you set program 1 OFF time, you press PROGRAM button again until 1 and OFF display.
Release Program button.
Then select hour, minute and days. In this case you want all days of week, so you keep pressing DAYs button until whole week displays: Mo Tu We Th Fr Sa Su

If you set ON time for all days of week, and OFF time for Tu Tuesday, then timer will not work correctly.

5) Read manual and add a comment for additional help

FM1D single-channel timer is difficult to program.
Open following links to identify timer and download manual:
http://waterheatertimer.org/Intermatic-timers-and-manuals.html#GM40AVE
http://waterheatertimer.org/pdf/fmd-20-setpoint-programming-guide.pdf

Timer flowchart starts page 3.
First step is to select format and then set current time.
Format is asking if you want 24hour or 12 hour format:
12 hour is am and pm
24 hour is military time where 11pm at night is hour 23.
Current time is simply the time right now.

Next step is to set program 1 thru 20 (P01 P02 thru P20)
Start by pushing +/- until desired program displays
Each program is set for either ON or OFF.
There are 20 memories available: 10 ON and 10 OFF.
Not necessary to use all 20 memories.
You need to set at least 1 ON time and 1 OFF time.

Make chart of on-off schedule to avoid conflicts in programming: For example ON at 7am Monday and OFF at 9am all-days-of-week will cause timer not to function as expected.
Each ON time is set for hour, minute and day.
Each OFF time is set for hour, minute and day
Press menu to terminate programming.

Add a comment for specific help with this timer.

ET8215C is Astronomic time piece that can also be programmed for specific on-off time.
http://waterheatertimer.org/pdf/Intermatic-et8015c-.pdf
1) You can disable the astronomic function by inserting a jumper shown in manual, and then program individual on-off times.
2) You can extend either DST start-time or end-time by fudging on the current time setting. For example if you want timer to turn off 1 hour after normal sunrise, then set current time 1 hour ahead. Of course this means timer turns on 1 hour later in the evening.
3) You can extend astronomic on-off times slightly by changing astro zone
4) You can set exact astro times, but the default maximum is shown as 120 minutes.

Add a comment and say what you discover to solve the problem.

(A=LIGHT,B=MODE,C=START,D=RESET)
1.How to use the luminescence Any time indication,Press A the Luminescence will last for 3 seconds.
2.How to view date? Standar time indication, press C "month/ date" indication.
3.How to switch 12/24 hour systems In the normal mode, press B twice and press D twice ,then hold C until 24 hour system is actuated, then press B for recovering.
4.How to check alarm ring and alarm time? Standard time indication,press D alarm time indication.
5.How to set alarm time? Standard time indication,Press B twice. The hour area flickers,press C to set the hour. After setting hour ,press D,the minute area flickers, press C to set the minute. Last press B for recovering.
6.How to set alarm ring? In standard time indication mode ,Hold D then Press C this will toggle alarm symbol on & Off.
7.How to set Hourly Chime? In standard time indicationmode, Hold D then Press B DAY OF WEEK area toggle on and off.
8.How to use stopwatch(1/100 seconds) Press B,then Oress C for 1 timing; Press D for multiple timings. Press D once more to continue operation after multiple timing. Press D for 1 timing; press C once and press Dtwice for multiple timing. (1)Max range of the stopwatch is 23 hours 59 minutes 59 seconds. (2)When timing within 30 minutes, the watch indicates: minute/second/1/100 second (3)When timing beyond 30 minutes, the watch indicates:hour/minute/second
9.How to adjust time, date,day of week (1)Standard time indication,press B twice ,the second area flickers, pressC to adjust second. (2)Then press D the Minute area flickers,Press C to adjust minute. (3)Press D the hour flickers, press C to adjust hour. (4)Press D the Date flickers, press C to adjust date. (5)Press D the month area flickers, press C for adjustment. (6)Press D the Day of Week area flickers, press C for adjustment. Then press B for recovering.

try setting the date 1 week ahead on the DS and then see if you can walk 1 dog (do not go for the walk), then set the date back and see if it works. i set the date back once and could not walk my dogs.